An inlet manifold of an engine supplies an air and fuel mixture to one or more cylinders of the engine. When more cylinders are included in the engine, the manifold evenly distributes the air and fuel mixture among the multiple cylinders. A carburetor may mix the air and fuel. The carburetor may include an open pipe that passes through to the manifold and includes a venturi shape. That is, the open pipe narrows then widens to increase the speed of the air flowing through the carburetor. To regulate the flow of air a throttle valve, downstream of the venturi shape, may be opened or closed.
In addition, a choke valve at or near the manifold may be used to further regular the ratio of fuel or air. The choke valve may be adjusted to restrict the flow of air, creating a richer fuel to air mixture. The choke valve may be adjusted manually (e.g., by a lever). Some engines may automatically adjust the choke valve through a temperature controlled mechanism. These automatic choke valves are easy for the user to operate. However, temperature alone does not always provide the optimal setting for a choke valve.